Increased colonic motility in a rat model of irritable bowel syndrome is associated with up-regulation of L-type calcium channels in colonic smooth muscle cells

Objective This paper aimed to investigate the relationship between up-regulation of L-type calcium channels and altered motility disorder in a rat model of irritable bowel syndrome (IBS). Methods Male Sprague-Dawley rats were subjected to neonatal maternal separation (NMS) from postnatal day 2-14 or normal handling (NH), and used when weighted 250-300 g. Colonic smooth muscle contractions was studied in an organ bath system. L-type Ca²⁺ channel α_1c subunit expression in smooth muscles from rat colon were studied by immunofluorescence and Western blotting analysis. The intracellular calcium concentration ([Ca²⁺]_i) of enzymatically isolated single colonic smooth muscle cell was studied with laser confocal fluorescent microscopy. Results The fecal pellets during 1 h water avoidance stress (WAS) were significantly increased; the amplitude of spontaneous contractions and contractions induced by Bay K 8644 (10 nm-1 μm), KCl (10-60 mm) and ACh (100 nm-10 μm) were significantly increased in NMS rats, when comparing with that of NH rats. [Ca²⁺]i induced by Bay K 8644 (1 μm), KCl (40 mm), and ACh (10 μm) significantly increased in muscle cells of NMS rats than NH rats. Further, α_1c protein expression was significantly up-regulated in colonic smooth muscle of NMS rats than NH rats. Conclusion These results suggest that NMS lead to up-regulation of L-type Ca²⁺ channels expression in the colon, which contributes to the colonic motility disorder. Our findings provide direct evidence to help understanding the underlying mechanism of chronic stress-induced colonic motility disorder in IBS.